diff --git a/drivers/pci/probe.c b/drivers/pci/probe.c
index 59011ce..6258f6f 100644
--- a/drivers/pci/probe.c
+++ b/drivers/pci/probe.c
@@ -1788,13 +1788,33 @@
 struct pci_bus * __devinit pci_scan_root_bus(struct device *parent, int bus,
 		struct pci_ops *ops, void *sysdata, struct list_head *resources)
 {
+	struct pci_host_bridge_window *window;
+	bool found = false;
 	struct pci_bus *b;
+	int max;
+
+	list_for_each_entry(window, resources, list)
+		if (window->res->flags & IORESOURCE_BUS) {
+			found = true;
+			break;
+		}
 
 	b = pci_create_root_bus(parent, bus, ops, sysdata, resources);
 	if (!b)
 		return NULL;
 
-	b->busn_res.end = pci_scan_child_bus(b);
+	if (!found) {
+		dev_info(&b->dev,
+		 "No busn resource found for root bus, will use [bus %02x-ff]\n",
+			bus);
+		pci_bus_insert_busn_res(b, bus, 255);
+	}
+
+	max = pci_scan_child_bus(b);
+
+	if (!found)
+		pci_bus_update_busn_res_end(b, max);
+
 	pci_bus_add_devices(b);
 	return b;
 }